This invention relates to a measuring device comprising a detector for a quantity x to be measured, which detector is adapted to produce two measuring signals I.sub.1 and I.sub.2 which relate to the quantity x to be measured as x=(I.sub.1 -I.sub.2)/(I.sub.1 +I.sub.2). The further comprises a processing circuit for converting the measuring signals I.sub.1 and I.sub.2 into an output signal U(x) whose value depends on the quantity x to be measured.
An example of such a device is disclosed in Technisches Messen tm, 53, No. 7/8, pp. 1986, 286-292. Reference is made especially to FIG. 6 and the associated description. In the cited example the detector is formed by a position-sensitive detector (PSD) which produces two currents I.sub.1 and I.sub.2 as the measuring signals. The processing circuit comprises a subtractor circuit and an adder circuit which supply signals proportional to the difference I.sub.1 -I.sub.2 and the sum I.sub.1 +I.sub.2, respectively, of the measuring signals. The outputs of these circuits are connected to the inputs of an analog divider which supplies an output signal proportional to (I.sub.1 -I.sub.2)/(I.sub.1 +I.sub.2). It has been found that the cited processing circuit and similar processing circuits offer satisfactory results if the requirements imposed as regards speed and dynamic range of the measuring system are not particularly severe.